Evidence of long-distance transport in the sands of the Alimini beach

In the framework of the SIGIEC (Sistema di Gestione Integrata per l'Erosione Costiera) PON project, focused on the erosion of key shore areas in Calabria and Apulia, the coastal area in front of the Alimini lakes (Otranto, Apulia) has been selected for the absence of anthropic structures or activities. The beach is 7.5 kms long and lays against a calcarenitic bedrock. It is sandy, and characterized by a volcaniclastic fraction and a biogenic component. The internal stratigraphy of the beach deposits is based on the reconstruction of stratigraphic sections in trenches. Vertical boundary between black to dark- grey to greyand light-grey layersand/or laminae characterize the entire sequence. Samples insight each layers or set of laminae were analysed to obtain information on the waves regimes and hydraulic control on sedimentation. Grain-size analysis have been performed on each sample. On the 0.25 and 0.5 mm fraction polished thin sections have been observed under the optical microscope, and selected grains have been analysed by SEM-EDX. Highly rounded quartz, limestone fragments and feldspars grains prevail in the grey to light-grey layers whereas mafic componentmainly consists of clinopyroxene, brown to yellow garnet and amphibole; sporadic crystals of colorless garnet also occur. The dark layers contain the same minerals but with different proportions: pyroxene and brown garnets are the dominant phases, followed by colorless garnets, opaques, quartz and amphibole. Feldspars and limestone fragments are subordinate; few staurolite and titanite crystals also occur. SEM- EDX analyses showed that pyroxenes can be classified as diopside-augite. Two population of garnets can be distinguished: a brown to yellow population with melanitic composition, and a colorless group of piralspitic composition. As already suggested by previous studies (Delle Rose and Elia, 2008) melanite, amphiboles and clinopyroxenes are of volcanic origin and their source can be found in the Vulture volcanic. However, the presence of piralspitic garnet and staurolite cannot be reconducted to Vulture volcano. Rather, we suggest a provenance from the Fossa Bradanica and/or Apenninic Units. The source areas and the roundness of the grains suggest that the sediments have been transported by Ofanto River, draining the Apenninic units and the Fossa Bradanica sediments together with the volcanics of Mt. Vulture. The sediments arriving at the Ofanto mouth, about 300 km North of Alimini beach, are drifted along the coast towards South.